One type of heating device used in various industries comprises a heat exchanger housing having an inlet and an outlet for the liquid to flow through. A heater element bundle is mounted in the housing. The heater element bundle has a number of electrical resistance heater elements. Each heater element includes a metal tube, an electrical resistance coil within the tube and embedded in an insulation powder, and an exterior conductor pin secured to the end of the coil. The heater has at least one end located outside of the housing, that end having a header to which each tube is secured. The opposite end may also include a header or the tubes may be hairpin-shaped.
Voltage is applied to the conductor pins to create heat in the electrical resistance coils. The fluid flows over and through the bundle of heater elements and is heated as a result. Depending on the application, the quantity of fluid flowing through the housing may be fairly low. Also, the increase in temperature required may be quite high, such as 300 to 1200 degrees F. While these heaters work well, it would be desirable to improve the efficiency of electric heaters for high temperature increases of low flow rate fluids.